In a recordable/reproducible DVD-RAM disk, the inside of the disk is divided into a plurality of zones. The number of rotations is constant within each zone, but is different between different zones. In general, such a system is called a zone CLV. Each zone is divided into a plurality of sectors, and each sector is formed by a data recording region in which information can be recorded and an address region in which the address of the sector has been previously recorded. Another feature of this system is that the data recording region can extend over both a guiding groove region of the disk (hereinafter, referred to as “groove”) and a region between the guiding groove regions (hereinafter, referred to as “land”). Address information is recorded in address portions so that a pair of address portions are offset from each other and each address portion extends over the groove and the land.
In order to smoothly perform reproduction in the data recording region based on the above special format, a single wave corresponding to a divisional component of a clock component (hereinafter, referred to as a “wobble”) is formed in an address region and a data recording region while cutting a disk. When reproducing from the disk, the wave component is detected as a tracking error signal.
Hereinafter, a conventional optical disk recording/reproduction device will be described.
FIG. 11 is a block diagram of a conventional optical disk recording/reproducing device 700. In FIG. 11, reference numeral 1 denotes a motor; reference numeral 2 denotes an optical disk; reference numeral 3 denotes an optical head; reference numeral 4 denotes a reproduction signal/servo signal detection circuit for generating a reproduction signal, a focus error signal, and a tracking error signal from an output signal obtained from the optical head 3; reference numeral 5 denotes focus/tracking control means for controlling the optical head 3 by using a servo signal from the reproduction signal/servo signal detection circuit 4 and for controlling the motor 2; reference numeral 6 denotes a reproduction signal binarizing circuit for binarizing the reproduction signal; reference numeral 7 denotes a demodulator for demodulating the binarized reproduction signal to generate reproduction data; reference numeral 8 denotes a laser driving circuit for driving a laser which is a light source of the optical head 3; reference numeral 9 denotes a recording signal generation circuit for generating a signal for modulating laser light by the laser driving circuit based on the data obtained after modulation; reference numeral 10 denotes a modulator for modulating data to be recorded so as to generate a signal which is supplied to the recording signal generation circuit 9; reference numeral 11 denotes power control means for controlling the laser power during recording/reproduction of data; reference numeral 12 denotes a gate signal generator for generating various gate signals based on a clock of a reference clock generator 14; reference numeral 13 denotes an error correction/address detection device for detecting and correcting the error amount of the reproduction data demodulated by the demodulator 7 and for detecting an address in the same data sequence; reference numeral 14 denotes the reference clock generator for generating a reference clock for recording/reproduction of data; reference numeral 15 denotes a CPU which gives the error correction/address detection circuit a command to measure a BER (Bit Error Rate), which can set the power in the recording power setting means, and which manages a user interface.
Hereinafter, an operation of the optical disk recording/reproduction device 700 having the above structure will be described.
An output signal read out from the optical disk 2 by the optical head 3 is supplied to subsequent process circuits as a reproduction signal, a focus error signal, and a tracking error signal by the reproduction signal/servo signal detection circuit 4. The focus error signal and the tracking error signal are supplied to the focus/tracking control means 5. The optical head 3 is controlled by the focus/tracking control means 5 so as to follow the wavering of the disk surface and decentration of the disk. The reproduction signal is supplied to the reproduction signal binarizing circuit 6, and the binarized data sequence and a read clock which is in synchronization with the data are output to the demodulator 7. The reference clock generator 14 generates a reference clock which is necessary for modulating/demodulating data to be recorded/reproduced by this apparatus.
The demodulator 7 performs modulation using the supplied binarized data sequence and the read clock according to a demodulation rule, and outputs the demodulated data to the error correction/address detection device 13 using the reference clock. The output reproduction data is supplied to the subsequent error correction/address detection device 13, and an address position on a track is detected by the detection device 13. An address detection signal is supplied to the gate signal generator 12, and the gate signal generator 12 uses this signal as a position reference on the track to generate, using the gate signal, a signal which is necessary during recording/reproduction.
Data to be recorded is converted by the modulator 10 into a data sequence to be recorded according to a modulation rule. The data sequence obtained by the conversion is further converted by the recording signal generation circuit 9 into a signal for modulating laser light, and this signal is supplied to the laser driving circuit 8. The laser driving circuit 8 modulates the laser light which is a light source of the optical head 3 for recording data on the disk. The recording is performed at a recording power predetermined by the CPU 15.
An operation of the optical disk recording/reproducing device having the above structure when recording is performed in a sector of a DVD-RAM disk is described with reference to FIG. 12. Each zone of the DVD-RAM disk is divided into a plurality of sectors, and each sector includes a data recording region in which information can be recorded and an address region in which an address of the sector has been recorded. In FIG. 12, a reproduction signal from the disk is shown in FIG. 12(a); a corresponding tracking error signal is shown in FIG. 12(b); a read gate signal, which is a representative gate signal necessary for reproduction of data/address, is shown in FIG. 12(c); a detection signal of the address is shown in FIG. 12(d); a recording gate signal, which is another representative gate signal necessary for recording is shown in FIG. 12(e); and an operation gate signal of the modulator is shown in FIG. 12(g).
A signal read out through the optical head 3 is output by the reproduction signal/servo signal detection circuit 4 as a reproduction signal shown in FIG. 12(a) and a tracking error signal shown in FIG. 12(b).
Assuming that the number of rotations of a disk in a zone N is equal to a target number of rotations, a read gate signal for reading an address of a target sector L is activated at timing (c)-2 in FIG. 12(c) using an address detection signal for a sector previous to the target sector L in which data is to be recorded as a reference.
The demodulator 7 performs demodulation based on data from the reproduction signal binarizing circuit 6 and the read clock, and reading of an address is performed in the error correction/address detection device 13. When the address has been normally read out, the detection device 13 generates a signal as shown in FIG. 12(d), and the gate signal generator 12 uses this signal as a reference to activate a recording gate signal and a modulator operation start signal at timings (c)-1 and (f)-1, respectively, for recording data. In response to the modulator operation start signal, the laser driving circuit 8 is placed into a recording state, and accordingly, the modulator operation start signal is activated, whereby the modulation of data is started, and the recording signal generation circuit 9 generates a recording signal.
Now, a method for determining the recording power is described. As described above, in an apparatus for recording data, the power used for recording is generally set through learning.
FIG. 13 is a flowchart showing an example of learning of the recording power. Herein, an example of learning in a DVD-RAM is described. In the optical disk apparatus, two types of learning, i.e., learning for a recording power Popt and learning for an erasing power Peopt, are performed for setting the recording power.
At the beginning of a learning process for the recording power (S101-S103), an interim erasing power Pe1 an d an interim recording power Pw1 are provided. The recording power Pw1 is set to a value sufficiently lower than an optimum recording power, and the erasing power Pe1 is set to a value in the vicinity of a value specified in the specification. The apparatus performs recording in any sector at the recording power Pw1 which is sufficiently lower than an optimum recording power and the erasing power Pe1 which is in the vicinity of a value specified in the specification, and measurement of the BER (S105).
Next, it is determined whether or not the measured BER is smaller than a threshold C1 (S106). Since the recording power Pw1 is a low power as described above, it is determined that the measured value is greater than the threshold C1 (“No” in S106). Next, the apparatus sets the recording power to a value which is equal to the recording power Pw1 plus a recording power increase Pws (S107), and performs recording (S104), and measures the BER (S105). The apparatus repeats this process and obtains a recording power Pw when the BER becomes smaller than the threshold C1. The product of the obtained recording power Pw and a multiplying factor Cw is used as an optimum recording power Pwopt (S108).
Next, the apparatus uses the optimum recording power Pwopt determined as described above so as to obtain an optimum erasing power Peopt. In the learning process for the erasing power, the apparatus performs recording at the erasing power Pe1 which is in the vicinity of a value specified in the specification (S109), and measurement of the BER (S110). Then, it is determined whether or not the BER exceeds a threshold C2 (S111).
When the BER does not exceed the threshold C2, the erasing power Pe1 is reduced by an erasing power decrease Pes (S112), and the steps S109 and S110 are repeated. During these steps, the erasing power Pe when the BER exceeds the threshold C2 is obtained.
The obtained erasing power Pe is stored as an erasing power variable PeL (S113). The erasing power Pe is reset to the erasing power Pe1. Then, the recording is performed at the erasing power Pe1 (S114). Next, the BER is measured (S115). Then, it is determined whether or not the BER exceeds the threshold C2 (S116). When the BER does not exceed the threshold C2, a predetermined value Pes is added to the erasing power Pe (S117). The erasing power Pe when the BER exceeds the threshold C2 is obtained. The central value of the erasing power Pe when the BER exceeds the threshold C2 and the previously obtained erasing power variable PeL is assigned as an optimum erasing power Peopt (S118).
The above process is merely an example of the learning for recording power. Alternatively, it is possible to learn the recording power by reproducing a recorded signal, detecting the amplitude thereto, and optimizing the value of the amplitude.
The above process is performed between the error correction/address detection device 13 and the power control means 11, whereby an optimum recording power is determined.
FIG. 14 is a diagram for illustrating recording by the apparatus on a disk whose optimum recording power is 10 mW. The recording is performed while the laser power is controlled so that the output of the object lens is 10 mW. In FIG. 14, in a portion on which a fingerprint is not attached, the transmissivity of a substrate layer is ideally 1, and accordingly, an effective recording power on a recording layer is 10 mW. As a result, optimum recording can be performed. However, as shown in the right side of FIG. 14, when a fingerprint, dust, or the like is attached on the substrate of the disk, the effective recording power on the recording layer is decreased according to the decrease in transmissivity due to the attachment. For example, when the transmissivity is decreased to 0.8, the recording power is decreased to 8 mW. As a result, optimum recording cannot be performed.
Next, reproduction of signal is described with reference to FIG. 15. The description is made with a reproduction signal appropriately recorded in the recording layer. In a portion on which a fingerprint or dust is attached, the transmissivity is 0.8, and the light amount decreases when the light reciprocates down and up through this portion. Assuming that the signal amplitude in a normal (clean) portion is 1, data in the dirty portion is reproduced at the following amplitude:(0.8)2=0.64 
Thus, in a portion on which a fingerprint, dust, or the like is attached, lack of the light amount and variation in the amplitude of the reproduction signal are caused. As a result, the attachment on the disk surface causes errors even when reproducing is performed on a portion in which appropriate recording has been performed.
The apparatus performs recording of data at the recording power determined by the above-described method. However, control for data recording is the control achieved by keeping the amount of laser light constant. Thus, in the apparatus having the above structure, when a fingerprint, a scratch, or the like is present on the substrate of the disk, or when the optical head 3 is subjected to vibration, impact, or the like, introduced from outside, defocusing or off-tracking is caused, and accordingly, the effective recording power on a recording film is reduced, whereby recording may not be normally performed.
This malfunction is described with reference to FIG. 16. Since the recording operation is performed as described above, the description thereof is omitted. In a sector in which recording is to be performed, when dirt, such as a fingerprint or the like, is present on the substrate as shown by the slanted lines in FIG. 16, the effective recording power in that portion is reduced. At this time, when a wobble signal is observed, the signal amplitude thereof is decreased in a portion on which dirt, such as a fingerprint, is present. Typically, the recording power margin of a rewritable optical disk is 10% to 30%. If the light amount is decreased to be smaller than the reduced effective recording power, recording cannot be correctly performed on the disk. Observing the reproduction signal waveform after the recording, the amplitude of the reproduction signal after the recording is reduced in a portion on which dirt, such as a fingerprint, is present. As a result, it becomes difficult to correctly reproduce data.
In summary, in a conventional apparatus structure, in recording data onto a DVD-RAM, there is a problem that recording by the apparatus cannot be appropriately performed due to a defect or dirt on a substrate of a disk, such as a fingerprint, a scratch, etc, or due to defocusing caused by a vibration/impact outside the optical head.